A plurality of electronic devices are powered via rechargeable batteries. Such devices include smartphones, portable gaming devices, tablet computers, portable music players, laptop computers, computer peripheral devices, communication devices (e.g., Bluetooth devices), digital cameras, and hearing aids, amongst others. While battery technology has improved, battery-powered electronic devices increasingly require and consume greater amounts of power, thereby often requiring recharging. Rechargeable devices are often charged via wired connections through cables or other similar connectors that are physically connected to a power supply.
Wireless charging technology has been developed and used for electronic devices in an effort to solve problems presented by wired charging solutions, such as contamination of contact terminals and moisture preventing the appropriate charging of the battery in the electronic device. Wireless charging systems may be capable of transferring power in free space and provide power to electronic devices or can be used to charge rechargeable electronic devices. Wireless power transmission is performed through a transmitter and a receiver coupled to the electronic device to be charged. The receiver antenna collects the radiated power from the transmitter and rectifies it for charging the battery.
Power converters are used to interface between power sources and electronic devices. Because alternating current is preferred for efficient power transmission, power sources typically provide power at alternating current. On the other hand the operation of many electronic devices requires direct current. In order to provide direct current for such devices from alternating current provided by the power sources, power converters need to convert the current supplied from alternating to direct, and use rectifiers for this purpose.
Half-bridge rectifiers are commonly used in power converters to provide half-wave rectification of alternating current. A typical half-bridge rectifier include two diodes which are inherently inefficient conductors producing a number of well-known problems. One problem resulting from the inefficiency of diodes is that they produce a forward voltage drop. This is most noticeable in low-voltage power converters where the voltage drop may be a significant proportion of the desired voltage output. Schottky diodes, which exhibit very low voltage drops, are often used to minimize the problem, but are an expensive solution. Conventional half-wave bridge rectifiers utilize junction diodes which show a forward bias voltage drop of approximately 0.7V. Thus, for a half-wave bridge rectifier, the resulting voltage drop relative to the input voltage can be as high as 1.4 volts. Another problem results from the heat dissipated by diodes, particularly in high frequency switching power supplies. Apart from reducing overall efficiency of the power converter, resulting high temperatures also reduce the reliability of components. Thus, additional design effort may be required to overcome the problems, and other factors such as the dimensions of the system may be affected as a result.
As such, there is a need for synchronous rectifiers characterized by low power loss characteristics and low associated heat loss for wireless power transfer systems that efficiently and safely transfer power at varying power levels to increase power transmission efficiency to electronic devices.